— 106 
or r = (2 1 ) ~ sec 
¢ 7 = ( 2 ^- 1 ) * 
and C n = (2 ?i— 3 ) ~ 
wliere n r (not less than - 2 ~j is tlio number at the leeward end of tlio member con- 
sidered, and E\ has tho same value as in the last chapter. The first group of 
equations is to bo used when the panel length is less than eighteen feet, and the 
second group for all other cases. As before Cn represents tho stress in tlie lower 
lateral strut at tlia free cml of tlio span. These stresses for all practical cases are 
given in Tublc V. 
The method of calculating the stresses in the vertical sway bracing is as fol- 
lows : the part relating to siiiglo track bridges' is essen Ü* 1113 r the same as given by 
Prof. Wm II. Burr in his treatise on “ Stresses in Bridge and 110 of Trusses” Tlio 
loads assumotl, uuless otherwise stated, are those obtained tincler a maximum wind 
pressure upon the empty bridge. 
In Fig. 1 let r be the pressure concentrated at the upper panel point on one 
side of the bridge : it is tliat which comes upon a panel length of top chord, one 
half tlie area of tlie diagonals meeting at the panel point wlien the truss is single 
intersection or one fourtli of said area when tlie truss is double intersection, and tlie 
portion of tho post above tlio piano A B. Let P’ be tlie pressure conceuti-ated at ono 
end of tlio intennediiito strut J K : it is that 
wliicli comes upon oue half of tlie post or the 
portion between tlie planes A B and C D, 
the latter being half way between J K and 
E F ; also, in double intersection bridge«, 
that which comes upon one half tlie area of 
tlie main diagonals and counters coupled at 
K, wliicli point would then be midway bet- 
ween H and F. 
Tlie pressures concentrated at the feet 
tlie posts tlo not affect tUo vertical sway bra- 
cing, so arc not considered. 
Let d f /, b and Q reprksent the measure* 
ments indicated in Eig. 1 
The total pressure 2 (P +P')=H is assu- 
med to be equally resisted by tlio feet of the 
posts : this assumption is probably as correct as any other that can be made. 
Taking the centre of niomonts at E, the moment of the pressure is 
2 P d + 2 P f (d—f) 
* These stresses are figured as if the loads JEi were concentrated on the chord nearest the 
coucave side of the track. This assumption was made so as to provide for the worst possible dis- 
tribution, because the exact method of divxsiou is unknown. 
